Circuit interrupter construction



June 3, 1952 UNDELL r 2,599,187

CIRCUIT INTERRUPTER CONSTRUCTION Filed May 28, 1949 3 Sheets-Sheet l lg,17 Il i i mmviozzs. l; 5 urd [b BY C Mei/i Bah/er,

June 3, 1952 s, ETAL 2,599,187

CIRCUIT INTERRUPTER CONSTRUCTION Filed May 28, 1949 3 Sheets-Sheet 2INVENTO fi gzzrd [Luzcie/A J 1952 s. l. LlNDELL ETAL CIRCUIT INTERRUPTERCONSTRUCTION 3 Sheets-Sheet 3 Filed May 28, 1949 H l I/ lrlllfllllllllllIlllllI/l Patented June 3, 1952 CIRCUIT IN TERRUPTER CONSTRUCTIONSigurd I. Lindell, Chicago, and Charles H. Baker,

Maywood, 111., assignors to S & C Electric Company, Chicago, Ill., acorporation of Delaware 16 Claims.

This invention relates generally to circuit interrupters and it hasparticular relation to circuit interrupters having fusible elements andadapted for use on high voltage transmission lines, such as linesoperating at voltages of the order of 34,900 or 69,000 volts. However,it will be understood that the principles of construction disclosedherein can be-usedfor circuit interrupters operating at higher or lowervoltages as may be desired. The present invention constitutes certainimprovements over that disclosed in application Serial No. 663,832,filed April 22, 1946, now abandoned, by Sigurd I. Lindell and Charles H.Baker and assigned to the assignee of this application. The presentinvention is intended for use with the dropout fuse constructiondisclosed in application Serial No. 663,834, filed April 22, 1946, bySigurd I. Lindell and assigned to the assignee of this application. Thepresent invention may be used with the contact construction disclosed inapplication Serial No. 57,346, filed October 29, 1948, now Patent No.2,578,255, dated December 11, 1951, by Sigurd I. Lindell and assigned tothe assignee of this application.

Among the objects of this invention are: To balance the mechanicalcharacteristics of the interrupter housing to the end that theinterrupting capacity of the device is increased without rupturing anyof the parts forming the same; to accomplish this without increasing theweight of the device substantially; to increase the normal currentcarrying capacity of the interrupter so that it can conduct continuouslycurrents of the order of four hundred amperes without overheating; toprovide the largest cross sectional area for the exhaust passageconsistent with the minimum wall thickness of the housing; to hold theterminals within a fuse housing against displacement under severeoperating conditions and thus increase the interrupting capacity of thedevice; to provide a lightweight construction which may be handled by ahook stick or similar tool; to accomplish these purposes, in part, bythreading the terminals at the ends of the arcing chamber into thelining surrounding the same, the lining having relatively high strengthin tension; to secure the various terminals, conducting tubes andretaining members together by mechanical deformation rather than bythreading, soldering, or welding; and to secure these parts to the endsof the tubular housing which encloses the same in a similar manner.

Other objects of' this invention will, in part, be obvious and in partappear hereinafter.

Application May 28, 1949, Serial No. 96,034

This invention is disclosed in the embodiment thereof shown in theaccompanying drawings, and it comprises the features of construction,combination of elements and arrangement of parts which will beexemplified in the construction hereinafter set forth and the scope ofthe application of which will be indicated in the appended claims.

For a more complete understanding of the nature and scope of thisinvention, reference can be had to the following detailed description,taken together with the accompanyingv drawings, in which:

Figure 1 is a longitudinal sectional view of a circuit interrupterhousing constructed in accordance with this invention having a linerintermediate its ends in which is located a body of arc extinguishingmaterial;

Figures 2 through 8 are views illustrating different parts and differentsteps in the assembly of the tubular terminal means which is positionedin the upper end of the fuse housing shown in Figure 1;

Figures 9 through 13 are views illustrating different parts anddifferent steps in the assembly of the terminal means which isassociated with the lower end of the housing shown in Figure 1;

Figure 14 is a View, partly in side elevation and partly in sectionshowing the upper and lower terminal means assembled in the fuse housingshown in Figure 1; I

Figure 15A and Figure 1513, the latter being placed below the former,together constitute a longitudinal sectional view of the fuse housingand terminal means assembled in its ends together with a portion of theoperating mechanism for the fuse; and

Figure 16 is a view, partly in side elevation and partly in section,showing an additional portion of the operating mechanism in assembledrelation in the fuse housing.

As indicated hereinbefore the present invention is adapted particularlyfor use in a dropout fuse construction such as that disclosed in theaforesaid application Serial No. 663,834. Since the features andmechanism which have to do with the dropout construction form no part ofthe present invention, they are not described in detail herein. It willbe understood, however, that the present invention can be employedeither as a non-dropout fuse or a dropout fuse as may be desired. Thepresent invention has to do particularly with the construction andarrangement of the terminal means at the ends of the tubular fusehousing which are useful in reducing cost of construction and at thesame time reducing the weight of'the various parts while providing thenecessary mechanical strength and electrical contact engagement betweenthe several conducting parts. The mechanical design characteristics arebalanced so that advantage can b taken of the relatively high strengthof the housing to resist radial pressure by holding the terminals inposi-- tion in the ends of the housing in a new and improved manner whenthe device is subjected to the longitudinal stress incident tointerrupting high fault current.

Referring now particularly to Figure l of the drawings, it will be notedthat the reference character l designates a tubular housing which isformed preferably of a phenolic condensation product. Its end sections Hand G2 are reduced in diameter, as shown, for receiving certain parts oftubular terminal means which will be described in detail hereinafter.These end sections II and 12 also have external annular grooves l3 andI4 into which a portion of a flange can be deformed for holding tubularterminal means in fixed position on the ends of the housing it.

Within the housing Ill there is provided a liner l5 that is formed ofrelatively high strength insulating material such as fibre which istough and resilient under conditions of dynamic stress. The liner l5fits snugly within the housing It and it is secured or bonded thereto bysuitable adhesive means. It will be noted that the ends I? and it of theliner I5 are beveled or tapered and that these ends are spacedsubstantial distances from the corresponding ends of the housing H3. The

purpose for this construction, as disclosed in the aforesaid applicationSerial No. 663,832 is to permit the use of a terminal arrangement whichwill distribute more effectively the electrostatic stress which isdeveloped around the fuse housing It during and after circuitinterruption.

It will be observed that the ends of the liner l5 are internallythreaded as indicated at 19 and 2D. The purpose of these threads is topermit the attachment of the tubular terminal means at the ends of thefus housing I0 directly to the liner l5 so as to place the latter intension when the former are subjected to longitudinal stress resultingfrom the operation of the circuit interrupter as will be describedhereinafter. Additional special threads 21 are provided on the innersurface of the liner i5 for receiving cakes 22 of arc extinguishingmaterial such as boric acid which is compressed therein as disclosed inthe aforesaid Lindell and Baker application. The cakes 22 of arcextinguishing material have a centrally located bore 23 one end 24 ofwhich opens into an outflared throat 24. While it is preferred to useboric acid for the arc extinguishing material within the fibre liner [5,it will be understood that the fibre could be extended radially inwardlyto take the place of the cakes. 22 and to provide the bore 23.

Referring now particularly to Figures 2' through =8 of the drawings, iswill be observed that the referenc character 23, Figure 8, designates,generally, one of the two tubular terminal means which are employed inconjunction with the tubular housing Ill. The terminal means 23 isintended to be positioned in the upper end of the housing Ill as it isshown in Figure 1 of the drawings, and this assembly is illustrated inFigure 14. The parts making up the tubular terminal means 26 and theirmethodv of. assembly now will bev described.

Referring first to Figure 2, it will be observed that the referencecharacter 2'! designates, generally, a relatively thick-walled tubularterminal which may be formed of brass. At its lower end the terminal 2'!has external threads 23 which are arranged to be threaded into thethreads It in the upper end of the liner 15. Intermediate its ends theterminal 2'! has a beveled or tapered surface 29 which serves todistribute more uniformly the electrostatic stress referred to above.Also the terminal 21 has a reduced diameter surface 30 at its upper endthe lower portion of which is longitudinally knurled as indicated at 31for a purpose which will be apparent presently. An external annulargroove 32 is provided in the knurled surface 3| and its function alsowill be set forth presently. Within the tubular terminal 21 there islocated a contact finger tube, shown generally at 33, that is formedpreferably of copper. The tube 33 is shown in Figure 3 and its assemblywith the tubular terminal 21 is shown in Figure 4. The contact fingertube 33 includes a plurality of flexible fingers 34 the upper ends orwhich are curved inwardly as indicated at 35 for receiving a garterspring 33, Figure 15A, and also'for making line contact with a contactmember which will be described hereinafter.

The lower end of the contact finger tube 33 is knurled longitudinally asindicated at 31 and this knurled portion is arranged to have a press fitwith the inner surface of a shoulder 33 which is formed integrally withand extends radially inwardly from the lower end of the tubular terminal27. The knurled portion 31 having a press fit with the inner surface ofthe shoulder 38 establishes multiple line contact between these parts.It will be noted that the shoulder 38 has an internal annular groove 39and that the lower end of the contact finger tube 33 intermediate theknurled surface 31 thereof is radially outwardly deformed thereinto asindicated at Ml. The deforming operation is performed preferably by asuitable rolling die.

The knurled and rolled construction just described for interconnectingthe contact finger tube 33 and the tubular terminal 31 both mechanicallyand electrically has several advantages. Because of the longitudinalknurling 3'! intimate electrical and mechanical contact engagement ishad with the inner surface of the shoulder 38. Multiple line contactunder pressure is obtained. At the same time because of this knurling itis unnecessary to maintain very close tolerances between the dimensionsof these parts and it is still possible to obtain the desired closeelectrical and mechanical engagement therebetween by a press fit Withoutrequiring that the usual close tolerances be maintained where theknurling is omitted. By deforming the knurled surface 31 as indicated at40 into the internal annular groove 39, the contact finger tube 33 isfixed securely in place in the tubular terminal 31. It will be apparentthat this method of joining the contact finger tube 33 to the tubularterminal 21 requires no threads and no soldering or welding and thathigh mechanical strength and good electrical contact are obtained. Ifdesired, the parts may be silver plated in order to further improve theconducting characteristics of the joint therebetween. It will beunderstood that this method of assembly is employed for joining othermetallic parts with the same advantages and this will be apparent as thedescription proceeds.

It will be noted in Figure 4 that the tubular terminal 21 has twoopenings 4! extending flared throat 24. The assembly of the tubularterminal 6 I, metallic tube 61 and retaining member H is then placed inthe housing ID with liner so that threads 62 of the tubular terminal 6|engage inner threads of the fibre liner. This assembly then is rotateduntil pressure is exerted upon the fibre exhaust ring 59 and lowermostinsulating cake 22 to provide a unitary assembly the inner surface ofwhich is smooth and will not impede the flow of gases from the bore 23,and which assembly prevents breakage of the cakes 22 of boric acid,

Instead of providing the retaining member H with an integrally formedflange, such as the flange 44, Figure 5, which forms a part of retainingmember 43, there is provided a separate member in the form of an exhaustferrule or tube, preferably formed of brass, and illustrated generallyat H in Figure 13. The exhaust ferrule or tube T! has internally spacedapart longitudinally knurled surfaces 18 and '19. As shown in Figure 14the exhaust ferrule or tube 11 is arranged to be telescoped over theretaining member 'H and over the end section (2 of the lower end of thetubular housing I9 so that the knurled portion 18 of the ferrule or tube1'! engages the external surface of H and the uppermost inner surface offerrule or tube TI is in press fit contact with the external surface ofhousing I0. Thereafter the exhaust ferrule or tube 11 is deformed asindicated at 80 and 8! by a suitable rolling die so as to interfit withthe annular outer groove 12 of the retaining member H and groove I4 inthe housing 10. Here again it is pointed out that the desired mechanicaland electrical connection between the parts 11 and H is provided by thecombination of the knurled surface 18 and the deformed portion 80 of theexhaust ferrule or tube 11 into the annular groove 12.

With a view to providing additional body for the exhaust ferrule or tube1'! so as to facilitate the attachment thereto of suitable terminalfittings by screws or the like, a bushing 82, preferably in the form ofa brass ring, is inserted therein and has a press fit with thelongitudinally knurled surface 19. It will be understood that thebushing 82 is assembled in the outer ferrule or tube 11 prior to itsassembly with the retaining member H and tubular housing I0.

The tubular housing 10 with the tubular terminal means 29 and assembledtherein, as shown in Figure 14, constitutes a subassembly in the stepsleading up to the complete assembly of the circuit interrupter. Next theflexible conductor 53 is threaded over a pulley 85, Figure 15A, which iscarried by a pulley yoke 86. The terminal 54 is threaded into the upperend of the rod-like terminal 55 which has a cylindrical contact section81 for engaging the upper ends of the contact fingers 34 of the contactfinger tube 33. The lower end 88 of the rod-like terminal 55 is reducedsomewhat in diameter, as shown, and it extends through the bore 23 inthe cakes 22 of arc extinguishing material. At its lower end the section88 is connected by a strain wire 89 and a fusible wire 90 to a terminal9| which projects through a spider 92 and is secured thereto by nuts 93.The spider 92 is formed of a suitable high conductivity material havingresilient qualities, such as hard drawn copper, and it bears against ashoulder 94 on the tubular terminal 6| as shown. It will be understoodthat the spider 92 is not rigidly attached to the terminal 6| so that,when suffieient pressure is generated as a result of the blowing of thefusible and strain wires 89 and 90, the spider 92 and the terminal 9|are blown outwardly through the metallic tube 61.

A coil compression spring 95 now is telescoped over the pulley yoke 86,pulley and flexible conductor 53, as shown in Figure 15A. Thereafter acompression tube 96 is telescoped over these same elements and isinserted into the metallic tube 48 at the upper end of the tubularhousing III as shown in Figure 16. By means of a suitable tool thepulley yoke 86 is held in an upright posi tion while the compressiontube 96 is moved inwardly to compress the spring 95 and is movedsufiiciently far so as to permit the insertion of a pulley bar 91underneath the upper end of the yokeBG which, when released, bearsagainst a shoulder 98 of an end ring 99 that is carried by the upper endof the compression tube 99. A screw I00 serves to rigidly interconnectthe pulley yoke 86 and the pulley bar 91. It will be understood that thecoil compression spring 95, acting through the compression tube 96 andthe pulley 85, places the flexible conductor 52 under tension. Thistension is transmitted by the rod-like terminal 55 to the strain element89, Figure 1513, which in turn transmits it to the terminal 9| that iscarried by the spider 92. The spider 92, since it reacts against theshoulder 94 of the tubular terminal 6 l, holds the spring 95 in thecompressed position as shown in Figure 16.

When the circuit interrupter, described hereinbefore, is subjected to apredetermined overload suflicient to cause the blowing of the fusiblewire and thereafter the strain wire 89, the spring no longer isrestrained and it moves the compression tube 96 upward. This causes therodlike terminal 55 and its reduced diameter section 88 to move upwardlythrough the bore 23 at a speed which is twice that of the movement ofthe compression tube 96. The are is drawn and extended into the bore 23in a manner well known and are extinguishing material is evolved fromits walls which serves to deionize the arc space and to assist inextinguishing the are. If the pressure is great enough, the terminal 9|and the spider 92 will be blown out of the metallic tube 51.

It will be understood that the retaining member or ferrule 43 and theexhaust ferrule or tube 11 are arranged and constructed so as to receivefittings, such as those disclosed in application Serial No. 663,834referred to above, for mounting the device in a dropout fuse mounting.As there disclosed, provision can be made for utilizing the upwardmovement of the compression tube 96 to unlatch the device and permit itto swing downwardly to an Open position. Also it will be understood thatthe exhaust ferrule or tube H is located at the lower or hinge end ofsuch a dropout device and it is for this reason that the specialconstruction thereof described hereinbefore is employed.

For illustrative purposes it is pointed out that. for a 69,000 voltcircuit interrupter, the tubular housing It] may be 35% inches long,with an outside maximum diameter of 2 inches and an internal diameter atthe ends varying from 1.682 to 1.713 inches. The fibre tube !5 isnineteen inches long. The terminal means 2-5 extends into the housing IDfrom the top 12% inches and the terminal means 60 extends into thehousing [3 from the bottom 7%};- inches.

As indicated hereinbefore the housing it, with the parts assembledtherein as shown and described, is supported by the exhaust ferrule ortube T! on the dropout mounting therefor. It is this lower end of thehousing It) that is held stationary when the device operates. When afault current of a relatively high magnitude is interrupted, the exhaustblast through the bore 23 and the tube 61 reacts like a jet in a jetpropulsion device. Since the housing I is fastened at its lower end andthe terminal means 25 and 69 are held in place, the resulting upwardthrust causes a tension stress to be developed in the housing It and inthe fibre liner l5. At the same time force is applied radially of theboric acid cakes 22 and the fibre liner l5. Because of the tough andresilient character of the latter, this radial force is resisted. Theterminal means 26 and 6d are prevented from being torn off since thetubular terminals 21 and El thereof are threaded into the fibre liner land the flange 44 and the ferrule H are secured to the ends of thehousing It in the grooves I3 and M as described. lhe cakes 22 of boricacid are held stationary and in compression by this construction. Thisis important since arc extinguishing gas is evolved from the bore 23 andit is most effective when it intimately contacts the arc drawn'from thelower 88 of the receding terminal 55.

Under severe interrupting conditions, the rodlilre terminal 55 is drivenupwardly at high speed. Its movement is arrested and the kinetic energythereof dissipated through force transmitted to the housing iii andliner [5 through the tubular terminal means 25. This force adds to thepreviously described force resulting from jet action developing thetension stress in the housing liner l5. Also under such operatingconditions the bore 2-3 may become eroded as a result of the flow ofseveral cycles of arc current and the blast action thereon developsadditional endwise thrust.

Under certain operating conditions the arc may restrihe in the bore 23after it has once been extinguished. An abrupt generation of pressureresults which is accompanied by severe longitudinal and radial stressesbeing created in the housing It and liner [5.

The circuit interrupter constructed and assembled as described iscapable of withstanding these stresses without disintegration for valuesof fault current greatly exceeding those which can be interrupted bydevices not so made. Further the present invention provides the largestpossible cross section for the exhaust opening through the tube ii! ofthe lower terminal means 60 consistent with the minimum wall thicknessof the housing iii so as to control the dielectric stress in thesurrounding air as described in the aforesaid application of Lindell andBaker. A similar relationship is provided for the tube 48, which forms apart of the upper terminal means 2%, and the adjacent portion of thehousing l0.

Since certain changes can be made in the foregoing construction anddifferent embodiments of the invention can be made without departingfrom the spirit and scope thereof, it is intended that all matter shownin the accompanying drawings and described hereinbefore shall beinterpreted as illustrative and not in a limiting sense.

What is claimed as new is:

1. In a high voltage circuit interrupter, in combination, a tubularhousing of insulating material, a liner of insulating material inside ofand secured to said housing, tubular terminal means extending into eachend of said housing with its inner end threaded into said liner, andmeans for drawing and extinguishing an arc in said liner including meanscapable of evolving a gaseous are extinguishing medium due to the heatof the are which expands endwise of said liner, the internal forcesresulting from pressure generated by said gaseous arc extinguishingmedium on circuit interruption tending to separate said tubular terminalmeans and place said liner in tension being resisted by the aforesaidconstruction whereby said terminal means are held stationary and theinterrupting capacity is increased.

2. In a high voltage circuit interrupter, in combination, a tubularhousing of insulating material, a liner of insulating material inside ofand secured to said housing; tubular terminal means extending into eachend of said housing and comprising an externally threaded tubularterminal threaded into said liner, and a metallic tube telescoped at itsinner end with and mechanically secured to said tubular terminal; andmeans for drawing and extinguishing an arc in said liner including meanscapable of evolving a gaseous arc extinguishing medium due to the heatof the are which expands endwise of said liner, the internal forcesresulting from pressure generated by said gaseous arc extinguishingmedium on circuit interruption tending to separate said tubular terminalmeans and place said liner in tension being resisted by the aforesaidconstruction whereby said terminal means are held stationary and theinterrupting capacity is increased.

3. In a high voltage circuit interrupter, in combination, a tubularhousing of insulating material, a liner of insulating material inside ofand secured to said housing; tubular terminal means extending into eachend of said housing and comprising an externally threaded tubularterminal threaded into said liner, and a metallic tube telescoped at itsinner end with and mechanically secured to said tubular terminal andextending out of the corresponding end of said housing; means securingthe projecting end of each metallic tube to said housing, and means fordrawing and extinguishing the arc in said liner includin means capableof evolving a gaseous arc extinguishing medium due to the heat of theare which expands endwise of said liner, the internal forces resultingfrom pressure generated by said gaseous are extinguishing medium oncircuit interruption tending to separate said tubular terminal means andplace said liner in tension being resisted by the aforesaid constructionwhereby said terminal means are held stationary and the interruptingcapacity is increased.

4. In a high voltage circuit interrupter, in combination, a tubularhousing of insulatin material having an external annular groove neareach end, a liner of insulating material inside of and secured to saidhousing with its ends internally threaded and spaced from the ends ofsaid housing; tubular terminal means extending into each end of saidhousing and comprising an externally threaded tubular terminal threadedinto the corresponding end of said liner, a metallic tube telescoped atits inner end with and mechanically secured to said tubular terminal andextending out of the corresponding end of said housing, and a retainingmember telescoped with and mechanically secured to the end of said tubeprojecting from said housing and having a flange telescoped with thecorresponding end of said housing and interfitting with the externalannular groove thereat; and means for drawing and extinguishing an arcin said liner including means capable of evolving a gaseous areextinguishing medium due to the heat of the are which expands endwise ofsaid liner, the endwise thrust resulting from pressure generated by saidgaseous arc extinguishing medium on circuit interruption being appliedto said tubular terminals and transmitted thereby to said housing andsaid liner to place both in tension whereby said terminals are heldstationary and the interrupting capacity is increased.

5. The invention, as set forth in claim 4, wherein a portion of theexternal surface of each tubular terminal coextensive with the metallictube and a portion of the external surface of each metallic tubecoextensive with each retaining member is knurled and the parts have apress fit.

6. The invention, as set forth in claim 5, wherein each tubular terminalhas an external annular groove in the knurled portion into which themetallic tube is deformed and each retaining member has an internalannular groove into which an intermediate part of the knurled surface ofsaid metallic tube is deformed.

'7. The invention, as set forth in claim 4, wherein each retainingmember is annular with an internal annular groove into which theassociated metallic tube is deformed and has a flange telescoped withthe adjacent end of the tubular housing and deformed into the annulargroove thereof.

8. The invention, as set forth in claim 7, wherein the flangeconstitutes an integral part of one retaining member and i separate fromthe other retaining member, and said other retaining member has anexternal annular groove into which its flange is deformed.

9. In a high voltage circuit interrupter, in combination, a tubularhousing of insulating ma terial having an external annular groove neareach end, a liner of insulating material inside of and bonded to saidhousing with its ends internally threaded and spaced from the ends ofsaid housing; tubular terminal means extending into each end of saidhousing and comprising an externally threaded tubular terminal threadedinto the corresponding end of said liner, a metallic tube telescoped atits inner end with and mechanically secured to said tubular terminal andextending out of the corresponding end of said housing, and a retainingmember telescoped with and mechanically secured to the end of said tubeprojecting from said housing and having a flange telescoped with thcorresponding end of said housing and interfitting with the externalannular groove thereat; a body of are extinguishing material within saidlining having a bore therethrough from which a gaseous are extinguishingmedium is evolved due to the heat of the are which expands endwise ofsaid liner, an expellable terminal bearing against one of said tubularterminals and adapted to be blown through its metallic tube on operationof the interrupter, a rod-like terminal extending through said bore,fusible means interconnecting said expellable terminal and said rod-liketerminal, flexible conducting means interconnecting said rodliketerminal and the other of said tubular terminals, and spring meanscooperating with said flexible conducting means to move said rod-liketerminal through said bore when said fusible means blows, the endwisethrust resulting from pressure generated by said gaseous arcextinguishing medium on blowing of said fusible means being applied tosaid tubular terminals and transmitted thereby to said housing and saidliner to place both in tension whereby said terminals are increased.

10. In a high voltage circuit interrupter for use with electric powersystems wherein the transient recovery voltage may be substantiallygreater than the normal frequency recovery voltage, in combination, atubular housing of insulating material having an arcing passagewayspaced from each end a distance several times the diameter of saidhousing, terminals at the ends of said housing for connection to thecircuit and between which said recovery voltages are applied, astationary metallic extension from each of said terminals inside saidhousing extending to the adjacent end of said arcing passageway, aninsulating tension member within said tubular housing mechanicallyinterlocked at its ends to the inner ends of said extensions to preventexpulsion of the same from said housing, and means for drawing an arc insaid passageway on operation of the interrupter, said extensions actingto distribute electrostatic stress between said terminals afterinterruption of current flow therebetween and prevent the dielectricstrength of said arcing passageway from rising above that of anyexternal parallel path between said terminals.

11. The invention, as set forth in claim 10, wherein the extensions aretubular and the insulating means mechanically interconnecting them is atube.

12. In a high voltage circuit interrupter for use with electric powersystems wherein the transient recovery voltage may be substantiallygreater than the normal frequency recovery voltage, in combination, atubular housing of insulating material having an arcing passagewayspaced from each end a distance several times the diameter of saidhousing, terminals at the ends of said housing for connection to thecircuit and between which said recovery voltages are applied, a tubularstationary metallic extension from each of said terminals inside saidhousing extending to the adjacent end of said arcing passageway, aninsulating tube having threaded connection at its ends to the inner endsof said tubular metallic extensions to prevent expulsion of the samefrom said housing, and means for drawing an arc in said passageway onoperation of the interrupter, said extensions acting to distributeelectrostatic stress between said terminals after interruption ofcurrent flow therebetween and prevent the dielectric strength of saidarcing passageway from rising above that of any external parallel pathbetween said terminals.

13. In a high voltage circuit interrupter, in combination, a relativelylong tubular housing of insulating material, a relatively short toughand resilient liner of insulating material within and substantiallymidway between the ends of and secured to said tubular housing, atubular terminal extending into each end of said housin with the innerend of each terminal mechanically interlocked with the adjacent end ofsaid liner and the outer end of each terminal mechanically interlockedwith the adjacent outer end of said housing, and means for drawing andextinguishing an arc within said tubular housing including a body ofmaterial capable of evolving a gaseous arc extinguishing medium due tothe heat of the arc, said body being secured to and disposed within saidliner and having a central bore whose diameter is substantially lessthan that of said liner, and a rod-like terminal filling said bore andmovable therethrough on the striking of an are at one end of said borebetween said rod-like terminal and the adjacent tubular terminal andremote from the ends of said tubular housing,

the endwise force resulting from pressure generated by said gaseous arcextinguishing medium and reacting against said body being resisted bythe aforesaid construction whereby said tubular terminals are heldstationary.

14. The invention, as. set forth in claim 13, wherein the tubularhousing is formed of a phenolic condensation product and the liner isformed of fibre.

15. In a high voltage circuit interrupter for'use with electric powersystems wherein the transient recovery voltage may be substantiallygreater than the normal frequency recovery voltage, in combination, atubular housing of insulating material having an arcing passagewayspaced from each end a distance several times the diameter of saidhousing, terminals rigidly secured to each end of said tubular housingand projecting beyond the same for connection to the circuit and betweenwhich said recovery voltages are applied, a stationary metallicextension from each of said terminals inside said housing extending tothe adjacent end of said arcing passageway and projecting beyond therespective end of said housing and rigidly secured to the terminalthereat, insulating tension means within said tubular housingmechanically interlocked at its ends to the inner ends of saidextensions to prevent expulsion of the same from said housing, and meansfor drawing an arc in said passageway on operation of the interrupter,said extensions acting to distribute electrostatic stress between saidterminals after interruption of current flow therebetween and preventthe dielectric strength of said arcing passageway from rising above thatof any external parallel path between said terminals.

16. In a high voltage circuit interrupter for use with electric powersystems wherein the transient recovery voltage may be substantiallygreater than the normal frequency recovery voltage, in combination, atubular housing of insulating material having an arcing passagewayspaced from 14 each end a distance several times the diameter of saidhousing, terminals rigidly secured to each end of said tubular housingand projecting beyond the same for connection to the circuit and betweenwhich said recovery voltages are applied, a stationary metallicextension from each of said terminals inside said housing extendingbeyond the respective end of said housing and rigidly secured to theterminal thereat and extending to the adjacent end of said arcingpassageway, means for drawing an are at one end of said arcingpassageway on operation of the interrupter including a stationaryterminal at said one end of said arcing passageway and a rod-liketerminal movable therethrough away from said stationary terminal,separate tubular insulating tension means within and secured to saidtubular housing and mechanically interlocked with the extension at saidone end of said arcing passageway away from which said rod-like terminalis movable to prevent expulsion of said extension from said housing,said extensions acting to distribute electrostatic stress between saidterminals after interruption of current flow therebetween and preventthe dielectric strength of said arcing passageway from rising above thatof any external parallel path between said terminals.

SIGURD I. LINDELL. CHARLES H. BAKER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,585,646 Bussmann May 25, 19261,762,766 De Garay June 10, 1930 1,811,277 Mosley June 23, 19312,208,440 Williams July 16, 1940 2,319,276 Triplett May 18, 19432,416,428 Boothe Feb. 25, 1947

